1. Field of the Invention
This invention relates to a fabrication method for a protective layer. More particularly, the invention relates to a fabrication method for a multi-layered thin film protective layer of a reflective micro liquid crystal display (μ-LCD) device.
2. Description of the Related Art
The operation of a reflective micro-LCD device is based on an application of a voltage to a metal layer on the surface of a control circuit. An electric field is generated to control the orientation of the liquid crystal. As light transmits through the liquid crystal and arrives to the metal layer, the metal layer reflects the light, which in turn transmits through the liquid crystal. The different orientations of the liquid crystal display different optical properties, thereby displaying different images.
During the packaging of the reflective μ-LCD device, the filling of the liquid crystal requires coating a spacer between the glass plate and the device wafer to separate the glass plate and the device wafer. In addition, a protective layer is formed on the metal layer of the device wafer surface to protect the underlying devices.
The spacer, however, can only be coated on the periphery of the device wafer. The glass plate supported by the spacer thereby bends easily at the center due to stress. As a result, while filling the liquid crystal, the thickness of the liquid crystal cannot be uniform, and a Newton's ring is resulted. The non-uniform thickness of the liquid crystal seriously affects the quality of the display. Not only the displaying color is changed, the differentiation between the shades of color is also reduced.
Further, the metal layer of the device wafer requires a protective layer to prevent the metal surface from moisture penetration and from being scratched. The structure and the thickness of the protective layer directly affect the reflection property of the metal layer. The fabrication of the protective layer is, therefore, a very critical step in the manufacturing of a reflective micro-LCD device.